Equity (Details) (USD $) In Millions, except Share data	1 Months Ended			3 Months Ended		6 Months Ended		1 Months Ended
	Mar. 31, 2011	Feb. 28, 2011	Jun. 30, 2011	Jun. 30, 2011 Common Stock [Member]	Jun. 30, 2010 Common Stock [Member]	Jun. 30, 2011 Common Stock [Member]	Jun. 30, 2010 Common Stock [Member]	Mar. 31, 2011 Series A Preferred Stock [Member]
Equity (Textuals) [Abstract]
Repurchase of common stock, shares				2,200,000	20,800,000	5,000,000	31,300,000
Repurchase of common stock, value				$ 191.3	$ 1,000.0	$ 386.6	$ 1,600.0
Series A Preferred Stock shares Redeemed								8,221
Total number of common stock shares issued on on conversion of Series A Preferred Stock	493,260
Preferred Stock, shares issued			0
Preferred Stock, shares outstanding			0
Common stock shares authorized for repurchase		20,000,000